A variety of health conditions, including birthweight, infections, wheezing and asthma, and type 1 diabetes (T1D) were considered. Randomized controlled trials (RCT’s) and relevant observational research were included in the review.

Birth weight

Only one RCT demonstrated a direct effect of vitamin D on extraskeletal outcomes of infants born to mothers who supplemented. In this Indian trial, two large doses of 600,000 IU of vitamin D were administered to pregnant mothers. Significant increases in birthweight, birth length, head and arm circumference, and skin fold thickness were observed.

When the observational studies are taken into consideration, the small and intermediate-sized studies found no effect of vitamin D on birthweight. One small, nested case control study found a U-shaped association between maternal 25(OH)D levels and birthweight in white women but not black women, suggesting that race-related polymorphisms in the vitamin D receptor (VDR) may exist. In larger observational studies, low maternal vitamin D status correlated with lower birthweights.

Infections

In children of HIV-infected women, low vitamin D status of the mother during pregnancy was associated with a 49% increased risk of mother-to-child transmission. At follow-up, children born to mothers with low vitamin D levels had a 61% greater risk of death.

The evidence for childhood respiratory infections was mixed.

Wheezing and asthma

Five large prospective cohorts and the majority of observational studies found an inverse association between maternal vitamin D intake and the risk of wheeze in children; the lower the level, the greater risk. Conversely, one study found a greater risk of asthma and eczema in children of mothers with higher 25(OH)D levels and another found a greater risk of allergies in children with higher vitamin D levels in cord blood at birth.

The authors note that on average, cord blood levels of vitamin D are 30% lower than the mother’s 25(OH)D level and any future guidelines for 25(OH)D status during pregnancy must take this into account.

Type 1 diabetes

Cod liver oil consumption (a source of vitamin D) had no association with T1D in offspring, but another study found an inverse link between maternal dietary vitamin D intake and T1D (not supplementation). Two other studies found significant reductions in T1D risk in offspring as a result of postnatal vitamin D supplementation and higher maternal 25(OH)D levels respectively.

In conclusion

The evidence for an association between the vitamin D status of the mother and extraskeletal effects of her children is mixed. Few RCTS exist and the ones that found no association used lower doses of vitamin D or had fewer cases of vitamin D deficiency among participants.

In general, larger observational studies were able to detect an effect of vitamin D, but the smaller and intermediate-sized studies were not. U-shaped associations were seen only in observational studies and not in RCT’s. There is great promise for the role of vitamin D in preventing HIV-transmission to children of infected mothers and the prevention of T1D. The conflicting evidence in allergies and asthma deserves further study, as does the influence of genetic polymorphisms of the VDR on health outcomes.

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